Synthesis gas (or syngas) is a mixture of hydrogen (H2) and carbon monoxide (CO) that can be obtained (in principle) from virtually any carbonaceous material, and may be utilized as a base material for the synthesis of a wide variety of commercially useful compounds, such as alcohols. Suitable carbonaceous materials for the production of syngas include both fossil resources (such as natural gas, petroleum, coal, and lignite) and renewable resources (such as lignocellulosic biomass and other carbon-rich waste materials). In many applications it may be preferable to use renewable resources for syngas production due to the rising economic and environmental impacts associated with exploitation of fossil fuel sources. There are a variety of technologies that may be used to convert such feedstocks into syngas, including steam reformation, pyrolysis, gasification, and/or partial oxidation of a carbon-containing feedstock.
Reactions similar to those of the well known Fischer-Tropsch synthesis, may be used to convert syngas into commercially useful alcohols. For example, U.S. Pat. No. 4,752,623 (to Stevens and Conway) discloses a cobalt/molybdenum/sulfur catalyst for producing mixed alcohols from syngas. Various investigators have explored formulations and manufacturing methods to improve the performance of such catalysts, as described in U.S. Patent Application No. 2010/331581 (to Kharas et al) and U.S. Patent Application No. US 2011/0319505 (to Janbroers et al). While mixed alcohol synthesis from syngas has been an area of intensive research and process development, fully developed technologies commercial technologies have not yet entered the market. This is due, at least in part, to the problem of catalyst stability and the generation of organosulfur compound contaminants during alcohol synthesis. These and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
In many systems and methods, mixed alcohol synthesis processes are facilitated by sulfided molybdenum catalysts. While sulfided catalysts are generally more active than their non-sulfided counterparts, reaction conditions in a mixed alcohol reactor will often lead to gradual loss of catalyst activity and the formation of various organosulfur compounds. While activity of such catalysts may be maintained by the addition of sulfur containing compounds to the syngas feed stream, as disclosed in U.S. Patent Application No. 2010/0280287 (to Kharas and May), addition of such compounds may exacerbate the problem of the formation of undesirable organosulfur compounds in the mixed alcohol synthesis reactor. These in turn appear in the reactor effluent and contaminate the mixed alcohol product stream.
Unfortunately, contaminating organosulfur compounds are often soluble in the alcohol products of such a reactor and in solvents utilized in removal of CO2 or acid gas waste. U.S. Patent Application No. 2011/0201701 (to Lucas et al) discloses adsorption techniques to remove such organosulfur compounds from an ethanol product stream. Another potentially useful technology for removal of organosulfur compounds is membrane separation, as disclosed in U.S. Patent Application No. 2010/0264065 (to Hamad and Bahamdan) and U.S. Patent Application No. 2011/0000823 (to Hamad). Both of these approaches, however, introduce considerable complexity to plant operations and may not give suitably complete removal of organosulfur compounds from the alcohol products. Additionally, if not removed beforehand, a portion of the organosulfur compounds may be passed into an acid gas removal unit of an alcohol absorber or similar product separation device placed downstream from the mixed alcohol reactor (for example, by an overhead vapor collector) where they tend to interfere with the recycling and reuse of materials used for acid gas removal, thereby increasing the cost and complexity of the system.
Thus, even though various systems and methods of mixed alcohol synthesis are known in the art, there is still a need for improved systems and methods, particularly those that address reduction or removal of organosulfur compounds.